Patients in emergency units or emergency departments of hospitals often present with suddenly developing, potentially life threatening conditions. The extent and the duration of said conditions are frequently unknown. The first steps of therapy are generally, and necessarily, directed at the support of the patient's vital functions such as mechanical ventilation, fluid supply, blood transfusion, defibrillation, external pacing or pharmacotherapy (for example, the administering epinephrine or vasopressin for low blood pressure; administering amiodarone, lidocaine, procainamide or magnesia sulphate for ventricular fibrillation; administering epinephrine, atropine or sodium bicarbonate for asystole). However, in most cases the impaired vital functions are only the symptom of another pre-existing condition. A successful therapy of the patient, thus, requires treatment of the cause underlying the acute condition. In cases of trauma the cause may be obvious. In other cases it may be more difficult to find.
In many cases, the underlying causes of a patient's symptoms (which may be life-threatening) are not readily apparent. For example, dyspnea can be caused by such diverse conditions as heart failure, pneumonia, sepsis, acute respiratory distress syndrome and pulmonary embolism. Syncope, the transient loss of consciousness and postural tone, may occur suddenly without warning or may be preceded by symptoms such as lightheadedness, dizziness, a feeling of warmth, nausea, diaphoresis and visual blurring. The ability of medical professionals to differentiate between syncope and seizure, for example, is important and in some cases difficult.
A pathophysiological mechanism underlying syncope is vasal dysregulation. Vasal dysregulation can have a variety of causes. For example, cardial causes include pulmonary embolism, acute myocardial infarction, cardiac arrhythmias (bradyarrhythmias as well as tachyarrhythmias) or hypertrophic obstructive cardiomyopathy. Syncope can also be caused by the activation of the parasympathetic nervous system which may be triggered by events such as painful or unpleasant stimuli, prolonged standing, rapid change from a reclining into an upright position, hyperthermia or urination. Another unspecific symptom that may be associated with life threatening conditions is acute chest discomfort. This symptom can be caused by stable angina, acute cardiovascular events (unstable angina or myocardial infarction), pulmonary embolism, peptic ulcer or pneumonia, for example.
Differential diagnosis takes into account the history of the patient and includes a clinical examination. These procedures may be time consuming and the administration of analgetics may reduce the diagnostic value of a clinical examination. Moreover, it is difficult or impossible to get information on history of the patient if the patient suffers from reduced consciousness or is mechanically ventilated. However, a rapid diagnosis allows a rapid initiation of a suitable therapy, reduces the suffering of the patient and increases his/her chances of survival.
Clinically, ischemic events (such as those described above) are characterized by pain, paleness of the skin, and weak or absent pulse in the affected area. Additionally, imaging methods may be used for the characterization of ischemic events, such as ultrasonography, computed tomography, magnetic resonance imaging (with and without contrast agent), angiography and scintigraphy may be used.
Circulatory complications may be detected by the presence of abnormal blood pressure. Occasionally, the presence of cardiac arrhythmia and acute cardiovascular events may be used as an additional indicator for circulatory complications. However, these and other known methods for detecting circulatory events do not allow for the diagnosis of temporary complications. Moreover, the methods known in the art do not yield quantitative information about the severity of a circulatory complication.
Symptoms and complications associated with ischemic events, for example, may be diagnosed with an initial evaluation of chest-pain patients including an electrocardiogram (ECG) and cardiac markers such as troponins. These tests, while specific, may be insensitive and can leave the requirement for further testing to achieve an accurate diagnosis. Other methods of diagnosis include magnetocardiography imaging which utilizes superconducting quantum interference devices to detect the weak magnetic fields generated by the heart's electrical fields (which utilizes the correlation between abnormal cardiac depolarisation or repolarisation and abnormality in the magnetic field map). Magnetocardiography imaging is approved by the Food and Drug Administration (FDA) as a safe device for the non-invasive detection of ischemia. However, in general these methods are generally, complicated, slow and not very sensitive.